EP0562488B1 - Superresolution scanning optical device - Google Patents

Superresolution scanning optical device Download PDF

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Publication number
EP0562488B1
EP0562488B1 EP93104561A EP93104561A EP0562488B1 EP 0562488 B1 EP0562488 B1 EP 0562488B1 EP 93104561 A EP93104561 A EP 93104561A EP 93104561 A EP93104561 A EP 93104561A EP 0562488 B1 EP0562488 B1 EP 0562488B1
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EP
European Patent Office
Prior art keywords
light source
superresolution
phase
area
light
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EP93104561A
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German (de)
English (en)
French (fr)
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EP0562488A1 (en
Inventor
Makoto Kato
Kenichi Kasazumi
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/123—Integrated head arrangements, e.g. with source and detectors mounted on the same substrate
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/0004—Microscopes specially adapted for specific applications
    • G02B21/002—Scanning microscopes
    • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
    • G02B21/0052—Optical details of the image generation
    • G02B21/0056—Optical details of the image generation based on optical coherence, e.g. phase-contrast arrangements, interference arrangements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/0004—Microscopes specially adapted for specific applications
    • G02B21/002—Scanning microscopes
    • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
    • G02B21/0052—Optical details of the image generation
    • G02B21/0072—Optical details of the image generation details concerning resolution or correction, including general design of CSOM objectives
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/58—Optics for apodization or superresolution; Optical synthetic aperture systems
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
    • G06K7/10554—Moving beam scanning
    • G06K7/10564—Light sources
    • G06K7/10574—Multiple sources
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
    • G06K7/10554—Moving beam scanning
    • G06K7/10594—Beam path
    • G06K7/10683—Arrangement of fixed elements
    • G06K7/10702—Particularities of propagating elements, e.g. lenses, mirrors
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • G11B7/1367—Stepped phase plates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1381—Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1387—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector using the near-field effect
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B2007/13727—Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing

Definitions

  • the present invention relates to (i) a superresolution scanning optical device, a laser scanning microscope, a bar-code scanner and a laser printer in each of which an object is scanned by a focused beam to optically process the information, (ii) an image forming optical device such as a disc device which has no scanning means but uses a semicoherent illumination, (iii) a stepper optical device used in a semiconductor producing process, and (iv) a superresolution light source device and a superresolution filter to be used in any of the optical devices above-mentioned.
  • the superresolution scanning optical device has scanning means for scanning a line or a space with a coherent beam focused in the form of a fine spot, and converting means for photoelectrically converting the light intensity of the scanned beams.
  • scanning and photoelectrically converting optical system there are proposed a variety of arrangements for effectively obtaining a fine spot equal to or smaller than the diffraction limit.
  • Fig. 19 schematically shows a conventional optical pickup head H proposed for effecting superresolution in an optical disk system
  • a conventional optical pickup head H proposed for effecting superresolution in an optical disk system
  • "High Density Optical Recording by Superresolution” Y. Yamanaka, Y. Hirose and K.Kubota, Proc. Int. Symp. on Optical Memory, 1989. Jap. J. of Appl. Phys., Vol. 28 (1989) supplement 28-3, pp. 197-200, see also "High density recording by superresolution in an optical disk memory system", Y. Yamanaka et al., Appl. Opt., Vol. 29, No. 20 (July 1990), pp. 3046-3051].
  • a coherent beam emitted from a light emitting point 10a from a coherent light source 10 comprising a semiconductor laser light source passes through a collimate lens 12, thus causing the coherent beam to be converted into parallel beam portions, each of which is then divided into two portions by a bi-refringent prism 14.
  • These beam portions penetrate a first beam splitter 16 and a second beam splitter 18, and are then focused in the form of a superresolution spot on a magneto-optical medium 22 by an objective lens 20.
  • beam portions as divided and reflected by the second beam splitter 18 transmit a condenser lens 24 and are intercepted at the side lobes thereof by a slit 26. Then, the beam portions transmit a condenser lens 28 and a Wollaston polarizing prism 30, and reach a first photodetector 32, where the beam portions are photoelectrically converted and read in terms of an electrical signal.
  • Beam portions as divided and passed through the first beam splitter 16 penetrate a condenser lens 34, and each beam portion is further divided into two portions by a third beam splitter 36. These two portions respectively reach a second photodetector 38 and a third photodetector 40, where servo signals for focusing and tracking are detected.
  • a knife edge 42 is disposed for cutting an edge of a beam portion which has penetrated the third beam slitter 36, and an actuator 43 is disposed for driving the objective lens 20.
  • Fig. 20 shows the principle of superresolution used in the optical pickup head H shown in Fig. 19. More specifically, two beams emitted from the bi-refringent prism 14 in Fig. 19 are equivalent to beams diffracted from two openings 44a, 44b formed in a light intercepting plate 44 in Fig. 20, and present an intensity distribution I(x) shown by a solid line on an image forming plane 46 (X-axis). A dotted line in Fig. 20 shows an intensity distribution I 0 (x) which would be obtained when either the opening 44a or 44b is present alone. It is well known that, since diffraction images from the openings 44a, 44b interfere with each other, there is formed an image of intensity distribution I(x) as shown by the solid line. In this case, the shape of each of the openings 44a, 44b (corresponding to the shape of the light emitting face of the Wollaston polarizing prism 30 in Fig. 19) may be in the form of a slit or a ring.
  • slit-like or annular openings are formed in a face equivalent to the opening face of the objective lens 20, and a predetermined phase and a predetermined amplitude transmissivity are given to each of the areas to obtain a fine spot smaller than that of the diffraction limit determined by the maximum opening of the objective lens 20.
  • the present invention is proposed with the object of providing a simple optical system capable of obtaining superresolution smaller than of the diffraction limit without the amount of light in the main lobe remarkably decreased.
  • a first superresolution scanning optical device comprises image forming means for forming the image of light from a coherent light source unit in the form of a fine spot on a conjugate face through an image forming optical system, and scanning means for scanning the fine spot formed on the conjugate face, the coherent light source unit having at least first and second light sources of which phases are reverse to each other, the first and second light sources having the relationship that the main lobe of the image of the second light source on the conjugate face is superposed on the lateral sides of the main lobe of the image of the first light source on the conjugate face.
  • the amplitudes of the lateral sides of the main lobe of the image of the first light source are cancelled by the amplitude of the main lobe of the image of the second light source, thus reducing the width of the main lobe of the image of the first light source. It is therefore possible to obtain superresolution smaller than the diffraction limit without slit-like or annular openings formed. Thus, with a simple optical system, superresolution can be achieved without the amount of light of the main lobe remarkably decreased.
  • the coherent light source unit may further include a third light source presenting the same phase as that of the first light source, and the second and third light sources may have the relationship that the main lobe of the image of the third light source on the conjugate face is superposed on the lateral sides of the main lobe of the image of the second light source on the conjugate face.
  • that remaining portion of the reverse phase component of the image of the second light source which has not been cancelled in the interference of the phase component of the image of the first light source with the reverse phase component of the image of the second light source is cancelled by the regular phase component of the image of the third light source. This reduces the amplitudes of the sub-lobes of the intensity distribution formed by the interference of the image of the first light source with the image of the second light source.
  • a first superresolution light source device for optical device comprises at least first and second light sources which are coherent with each other and which are reverse in phase, the first light source being disposed on the optical axis of an image forming optical system or in the vicinity of this optical axis, and the second light source being disposed in the vicinity of the first light source.
  • the amplitudes of the lateral sides of the main lobe of the image of the first light source are cancelled by the amplitude of the main lobe of the image of the second light source.
  • the second light source is smaller in output than the first light source.
  • the first superresolution light source device for optical device above-mentioned may further comprise a third light source which is coherent with the second light source and which has a phase reverse to that of the second light source, the third light source being located in the vicinity of and at the opposite side of the second light source with respect to the first light source.
  • a third light source which is coherent with the second light source and which has a phase reverse to that of the second light source, the third light source being located in the vicinity of and at the opposite side of the second light source with respect to the first light source.
  • the second light source is smaller in output than the first light source, and that the third light source is smaller in output than the second light source. This may further reduce the amplitudes of the sub-lobes of the intensity distribution formed by the interference of the images of the first and second light sources with each other.
  • a second superresolution light source device for optical device comprises a coherent light source for emitting a coherent beam, and a phase plate disposed in the vicinity of and opposite to a beam emitting part of the coherent light source for emitting a coherent beam, the phase plate having a first phase area for imparting a predetermined phase to a first area which is the center of a coherent beam emitted from the beam emitting part, and a second phase area for imparting a phase reverse to the predetermined phase to a second area outside of the first area of the coherent beam emitted from the beam emitting part.
  • the amplitudes of the lateral sides of the main lobe of the image of light having passed through the first phase area are cancelled by the amplitude of the main lobe of the image of light having passed through the second phase area, thus reducing the amplitude of the main lobe of the image of the light having passed through the first phase area. It is therefore possible to obtain superresolution smaller than the diffraction limit without slit-like or annular openings formed. Thus, superresolution may be achieved without the amount of light of the main lobe remarkably decreased.
  • the phase plate may be arranged such that an output of the second area of a coherent beam emitted from the beam emitting part is smaller than an output of the first area of the coherent beam.
  • the output of light having passed through the second phase area may be smaller than that of light having passed through the first phase area. Accordingly, there is reduced the amplitude of that remaining portion of the reverse phase component of the image of light having passed through the second phase area which has not been cancelled in the interference of the phase component of the image of light having passed through the first phase area with the reverse phase component of the image of the light having passed through the second phase area. This may reduce the amplitudes of the sub-lobes of the intensity distribution formed by the interference of the image of the light having passed through the first phase area with the image of the light having passed through the second phase area.
  • the first phase area of the phase plate may be circular and the second phase area of the phase plate may be annular, or the first phase area of the phase plate may be rectangular and the second phase area of the phase plate may be made in the form of a rectangular frame.
  • the phase plate may have a third phase area which imparts a phase reverse to that of the second phase area, to a third area outside of the second area of a coherent beam emitted from the beam emitting part.
  • that remaining portion of the reverse phase component of the image of light having passed through the second phase area which has not been cancelled in the interference of the phase component of the image of light having passed through the first phase area with the reverse phase component of the image of the light having passed through the second phase area may be cancelled by the regular phase component of the image of light having passed through the third phase area. This may reduce the amplitudes of the sub-lobes of the intensity distribution formed by the interference of the image of the light having passed through the first phase area with the image of the light having passed through the second phase area.
  • the phase plate may be arranged such that an output of the third area of a coherent beam emitted from the beam emitting part is smaller than an output of the second phase area of the coherent beam. In such an arrangement, there may be further reduced the amplitudes of the sub-lobes of the intensity distribution formed by the interference of the image of light having passed through the first phase area with the image of light having passed through the second phase area.
  • the third phase area of the phase plate is preferably annular when the first phase area of the phase plate is circular and the second phase area is annular.
  • the third phase area of the phase plate is preferably made in the form of a rectangular frame when the first phase area of the phase plate is rectangular and the second phase area is made in the form of a rectangular frame.
  • a first superresolution filter for optical device comprises a holographic optical element which has a hologram recorded on the surface thereof, the hologram presenting the waves of phase row light sources including first and second light sources from which lights are emitted in the form of waves of which phases are reverse to each other, the hologram being arranged such that, when diffracted light from the hologram is focused, a main lobe formed by the second light source is superposed on the lateral sides of a main lobe formed by the first light source.
  • a second superresolution filter for optical device in accordance with the present invention comprises a holographic optical element which has a hologram recorded on the surface thereof, the hologram presenting the waves of phase row light sources including first and second light sources from which lights are emitted in the form of waves of which phases are reverse to each other, and a third light source presenting a phase reverse to that of the second light source, the hologram being arranged such that, when diffracted light from the hologram is focused, a main lobe formed by the second light source is superposed on the lateral sides of a main lobe formed by the first light source, and a main lobe formed by the third light source is superposed on the lateral sides of a main lobe formed by the second light source.
  • a third superresolution filter for optical device comprises a holographic optical element which has a computer-synthesized hologram recorded on the surface thereof, the computer-synthesized hologram presenting the waves of phase row light sources including first and second light sources from which lights are emitted in the form of waves of which phases are reverse to each other, the waves being calculated as an inline-type Fourier transform hologram, the computer-synthesized hologram being arranged such that, when diffracted light from the hologram is focused, a main lobe formed by the second light source is superposed on the lateral sides of a main lobe formed by the first light source.
  • a fourth superresolution filter for optical device comprises a holographic optical element which has a computer-synthesized hologram recorded on the surface thereof, the hologram presenting the waves of phase row light sources including first and second light sources from which lights are emitted in the form of waves of which phases are reverse to each other, and a third light source presenting a phase reverse to that of the second light source, the waves being calculated as an inline-type Fourier transform hologram, the computer-synthesized hologram being arranged such that, when diffracted light from the hologram is focused, a main lobe formed by the second light source is superposed on the lateral sides of a main lobe formed by the first light source, and a main lobe formed by the third light source is superposed on the lateral sides of a main lobe formed by the second light source.
  • a second superresolution scanning optical device comprises a coherent light source, focusing means having a collimate lens for focusing a coherent beam emitted from the coherent light source on a recording surface of an optical disc, and control means for controlling the relative position of the focusing means with respect to the recording surface of the optical disc, the collimate lens having, in a unitary structure, any of the first to fourth superresolution filters for optical device above-mentioned.
  • a third superresolution scanning optical device comprises a coherent light source, focusing means having an objective lens for focusing a coherent beam emitted from the coherent light source on a recording surface of an optical disc, and control means for controlling the relative position of the focusing means with respect to the recording surface of the optical disc, the objective lens having, in a unitary structure, any of the first to fourth superresolution filters for optical device above-mentioned.
  • a fourth superresolution scanning optical device comprises a coherent light source and focusing means having a collimate lens, a polygon mirror and a focusing lens for focusing a coherent beam emitted from the coherent light source, the collimate lens having, in a unitary structure, any of the first to fourth superresolution filters for optical device above-mentioned.
  • a fifth superresolution scanning optical device comprises a coherent light source and focusing means having a collimate lens, a polygon mirror and a focusing lens for focusing a coherent beam emitted from the coherent light source, the focusing lens having, in a unitary structure, any of the first to fourth superresolution filters for optical device above-mentioned.
  • a superresolution scanning optical device in which a coherent beam emitted from the coherent light source is focused through the polygon mirror so that the amount of light of the main lobe of the light source image is not remarkably reduced.
  • Fig. 1 schematically shows the arrangement of an optical pickup head system in a superresolution scanning optical device in accordance with a first embodiment of the present invention.
  • a coherent light source 100 such as a semiconductor laser
  • a focusing lens 102 passes a collimate lens 106.
  • the light is reflected by a polarized beam splitter 108 and passed through a quarter wave plate 110, and is guided to an objective lens 112 and reaches an optical disc 114, where the image of the light is formed on a pit face thereof.
  • the light which has passed through the objective lens 112, the quarter wave plate 110 and the polarized beam splitter 108 impinges into a servo signal detecting holographic optical element (See Japanese Patent Laid-Open Publication No.
  • Fig. 2 (a) shows the arrangement in front elevation of the phase plate 104
  • Fig. 2 (b) shows the arrangement thereof in section taken along the line II-II in Fig. 2 (a).
  • Fig. 3 shows the state of a beam waist 126 (waist diameter: w) in the vicinity of the phase plate 104.
  • the phase plate 104 has an annular phase structure.
  • the phase plate 104 is provided on the surface thereof with a center zone 104a which comprises a circular convex and which serves as a first phase area, an intermediate zone 104b which comprises an annular concave formed outside of the center zone 104a and which serves as a second phase area, and an outer zone 104c which comprises an annular convex formed outside of the intermediate zone 104b and which serves as a third phase area.
  • An opaque layer 104d is formed outside of the outer zone 104c on the surface of the phase plate 104.
  • the center zone 104a and the outer zone 104c have the same height.
  • a difference in level d 1 Formed between the intermediate zone 104b and each of the center zone 104a and the outer zone 104c is a difference in level d 1 for generating a phase difference ⁇ between transmitted lights each having a wavelength ⁇ .
  • a light portion which passes through the intermediate zone 104b and a light portion which passes the center zone 104a are reverse in phase to each other, while a light portion which transmits the outer zone 104c and a light portion which transmits the intermediate zone 104b, are reverse in phase to each other.
  • Fig. 4 schematically shows the arrangement of an optical pickup head system in a superresolution scanning optical device in accordance with a second embodiment of the present invention.
  • the basic arrangement of this optical pickup head system is shown by ["Recent advances in optical pickup head with holographic optical elements", M.Kato et al., Proc. SPIE vol. 1507, pp. 4, EGO'91, Holographic Optics III: Principles and Applications, 11-15 March 1991, The Hague, The Netherlands].
  • a coherent light source 200 As shown in Fig. 4, light emitted from an emission point 200a (an active layer emission face having a slit-like opening formed in a semiconductor laser) of a coherent light source 200, is focused on a reflexion-type phase plate 204 by a condenser lens 202. Then, the light passes a collimate lens 206 and a servo signal detecting holographic optical element 208 similar to that used in the first embodiment. The light is then guided to an objective lens 210 and reaches an optical disc 212, where the image of the light is formed on a pit face thereof.
  • an emission point 200a an active layer emission face having a slit-like opening formed in a semiconductor laser
  • an actuator 217 is disposed for driving the servo signal detecting holographic optical element 208 and the objective lens 210, and there is also disposed a base stand 218 on which the coherent light source 200, the reflexion-type phase plate 204 and the photodetector 216 are integrally placed.
  • a superresolution light source and signal detecting device 220 is formed in an integrated manner by the coherent light source 200, the focusing lens 202, the reflexion-type phase plate 204, the collimating lens 206 and the photodetector 216 which have been discussed in the foregoing.
  • An optical pickup head device 222 is formed in an integrated manner by the superresolution light source and signal detecting device 220, the servo signal detecting holographic optical element 208 and the objective lens 210.
  • the coherent light source 200 has an arrangement of the surface emission type or an arrangement equivalent to the surface emission type.
  • Fig. 5 shows the structure of main portions of the base stand 218, and Fig. 6 shows the structure in section of the reflexion-type phase plate 204.
  • the reflexion-type phase plate 204 is formed on an inclined surface 224 of the base stand 218 which is inclined substantially at an angle of 45° with respect to the optical axis.
  • the reflexion-type phase plate 204 is provided on the surface thereof with a center zone 204a which comprises an elliptical convex and which serves as a first phase area, an intermediate zone 204b which comprises an elliptical annular concave formed outside of the center zone 204a and which serves as a second phase area, and an outer zone 204c which comprises an elliptical annular convex formed outside of the intermediate zone 204b and which serves as a third phase area.
  • a low reflection factor surface 204d is formed outside of the outer zone 204c on the surface of the reflexion-type phase plate 204.
  • the center zone 204a and the outer zone 204c have the same height.
  • a difference in level d 2 Formed between the intermediate zone 204b and each of the center zone 204a and the outer zone 204c is a difference in level d 2 for generating a phase difference ⁇ between transmitted lights each having a wavelength ⁇ .
  • the difference in level d 2 is about 0.07 ⁇ .
  • the center zone 204a, the intermediate zone 204b and the outer zone 204c form a reflection face.
  • a light portion which is reflected by the intermediate zone 204b and a light portion which is reflected by the center zone 204a are reverse in phase to each other, while a light portion which is reflected by the outer zone 204c and a light portion which is reflected by the intermediate zone 204b, are reverse in phase to each other.
  • Fig. 7 shows a superresolving operation with the use of, as a model, a double diffraction optical system represented by a wave formed on an aperture 312 of an optical system.
  • a superresolving operation can be used in a variety of scanning optical systems and can be readily extended to designing of an image forming optical system.
  • a double diffraction image of the first light source 301 alone is shown by a curve 301a (a complex amplitude distribution) and a curve 301i (an intensity distribution).
  • the second light source 302A, 302B is disposed in the vicinity of both sides of the first light source 301 with a phase ⁇ reverse to that of the first light source 301, a double diffraction image (a complex amplitude distribution) 302a of the second light source 302A is superposed on the double diffraction image 301a of the first light source 301 (a double diffraction image of the second light source 302B is not shown, but this is axially symmetric with respect to the double diffraction image 302a of the second light source 302A).
  • the third light source 303A, 303B is located in the vicinity of both sides of the second light source 302A, 302B with the same phase as that of the first light source 301, a double diffraction image (a complex amplitude distribution) 303a of the third light source 303A is coherently superposed in the same manner above-mentioned (a double diffraction image of the third light source 303B is not shown, but is axially symmetric with respect to the double diffraction image 303a of the third light source 303A).
  • u 2A (x) A +1 x (sin (x- ⁇ 1 )/(x- ⁇ 1 ))
  • u 2B (x) A -1 x (sin (x+ ⁇ 1 )/(x+ ⁇ 1 ))
  • u 3A (x) A +2 x (sin (x- ⁇ 2 )/(x- ⁇ 2 ))
  • u 3B (x) A -2 x (sin (x+ ⁇ 2 )/(x+ ⁇ 2 ))
  • a +1 , A -1 and A +2 , A -2 respectively refer to the relative amplitudes of the second light source 302A, 302B and the third light source 303A, 303B when the amplitude of the first light source 301 is normalized to 1.
  • x is equal to (a/( ⁇ x f)) x ⁇
  • a is the opening diameter of the aperture face 312
  • ⁇ 1 is the coordinates of the peak position in the complex amplitude distribution of the second light source 302A, 302B
  • ⁇ 2 is the coordinates of the peak position in the complex amplitude distribution of the third light source 303A, 303B
  • ⁇ is the wavelength of each light source
  • f is equal to f 2 (f 2 is the focal length of the objective lens 308, see Fig. 7), and ⁇ is the coordinates of the image forming face 310 in terms of real dimensions.
  • f 1 is the focal length of the focusing lens 306.
  • u (x) sin x/x +A +1 x (sin (x- ⁇ 1 )/(x- ⁇ 1 )) +A -1 x (sin (x+ ⁇ 1 )/(x+ ⁇ 1 )) +A +2 x (sin (x- ⁇ 2 )/(x- ⁇ 2 )) +A -2 x (sin (x+ ⁇ 2 )/(x+ ⁇ 2 ))
  • the intensity distribution 320 of the double diffraction image is reduced to about 1.1/1.4 (approximately 0.79) in half-width as compared with the distribution 330 above-mentioned (where the distribution obtained with the first light source 301 alone is multiplied by 0.73).
  • the rate of the amount of light distributed outside of the half-width is reduced as compared with the distribution 330 where the distribution obtained with the first light source 301 alone is multiplied by 0.73. Accordingly, there is eliminated a slit optical system (designated by 26 in Fig. 19) for restraining the side lobes which is used in a conventional superresolution optical system having a simple annular opening.
  • the main lobe size (the image obtained with a circular aperture is called an Airy pattern, of which diameter D is equal to 1.22 x a x (1/ ⁇ f) x ⁇ ) is greater by 1.22 time (when r is approximately 3.8, J 1 (r) is equal to 0).
  • the optimum layout of light source rows for producing a superresolution effect with a circular opening is slightly different from that with a rectangular aperture.
  • the amplitude ratio of the second light source to the first light source is set to 0.3
  • the amplitude ratio of the third light source to the first light source is set to about 0.15
  • Fig. 9 shows an example of the layout of light source rows.
  • each of the second light source 302 and the third light source 303 is so arranged as to appear in a discontinuous manner (in the form of islets).
  • Fig. 10 shows the arrangement of a first embodiment of a superresolution light source device which can be commonly used in the optical pickup head devices in accordance with the first and second embodiments of the present invention.
  • Fig. 11 shows the structure of the superresolution light source device in section taken along the line XI-XI in Fig. 10.
  • a phase plate 402 is disposed in the vicinity of an opening 400a in the light emission surface of a coherent light source 400 comprising a semiconductor laser. As shown in Fig. 11, the phase plate 402 includes a difference in level. More specifically, the phase plate 402 is provided on the surface thereof with a first phase area 402a comprising a rectangular convex, a second phase area 402b comprising a convex in the form of a rectangular frame formed outside of the first phase area 402a, and a third phase area 402c comprising a convex in the form of a rectangular frame formed outside of the second phase area 402b. An opaque area 402d is formed outside of the third phase area 402c on the surface of the phase plate 402.
  • the first phase area 402a and the third phase area 402c have the same level, and between each of the first and third phase areas 402a, 402c, and the second phase area 402b, there is formed a difference in level d 3 for generating a difference in phase ⁇ between transmitted lights each having a wavelength ⁇ .
  • light which penetrates the first phase area 402a serves as the first light source 301 in Fig. 7
  • light which transmits the second phase area 402b serves as the second light source 302A, 302B in Fig. 7
  • light which transmits the third phase area 402c serves as the third light source 303A, 303B in Fig. 7.
  • the diameter of a spot obtained by a scanning optical system using the superresolution light source device of the present invention can be reduced according to the principle discussed with reference to Fig. 7. Further, it becomes possible to improve the uneven spread of the diffraction angle, i.e., the phenomenon where ⁇ is greater than ⁇ in Fig. 10, that has been regarded as a defect in a conventional semiconductor laser, so that a great spread angle ⁇ ' can be obtained even in the x-axis direction. Further, it becomes possible to correct astigmatism of a semiconductor laser.
  • Fig. 12 shows the arrangement of a second embodiment of the superresolution light source device which can be commonly used in the optical pickup head devices mentioned earlier.
  • a phase film made of, for example, SiO 2 is formed on the light emission facet of a semiconductor laser 500 to form a one-dimensional grid-like phase area, thus forming a superresolution light source.
  • the semiconductor laser 500 is provided on the light emission facet thereof with a first phase area 502a in the form of a convex extending at right angles to a light emission opening 500a of the semiconductor laser 500, second phase areas 502b, each in the form of a concave, extending at both sides of and in parallel to the first phase area 502a, and third phase areas 502c, each in the form of a convex, formed outside of and in parallel with the second phase areas 502b.
  • the first phase area 502a and the third phase areas 502c have the same level, and between each of the first and third phase areas 502a, 502c and the second phase areas 502b, there is formed a difference in level d 4 for generating a difference in phase ⁇ between transmitted lights each having a wavelength ⁇ .
  • Fig. 13 shows a modification of the superresolution light source according to the second embodiment shown in Fig. 12.
  • a substrate 510 made of, for example, SiO 2 is provided on the surface thereof with first, second and third phase areas 512a, 512b, 512c which produce operational effects similar to those produced by the first, second and third phase areas 502a, 502b, 502c above-mentioned.
  • the substrate 510 is disposed opposite to the light emission face of a semiconductor laser 514.
  • Fig. 14 shows the principle of a holographic filter for superresolution which provides an equivalent of the superresolution light source device above-mentioned and which can be commonly used in the light pickup head devices according to the first and second embodiments of the present invention.
  • an interference pattern is recorded on a photosensitive plane 330.
  • distances between the respective points are extremely small of 10 -3 order (one thousandsth) as compared with the distance f 3 between the light source face 300 and the photosensitive face 330. Accordingly, there is obtained, on the photosensitive plane 330, an interference pattern of a kind of a lensless Fourier transform hologram.
  • an interference component of the points 301 and 302A with each other and an interference component of the points 301 and 302B with each other appear in the form of a curve 340 as the intensity distribution I ( ⁇ )
  • an interference component of the points 301 and 303A with each other and an inteference component of the points 301 and 303B with each other appear in the form of a curve 342.
  • Figs. 15 to 17 show a method of actually producing a superresolution holographic filter according to the holography above-mentioned.
  • a coherent beam emitted from a semiconductor laser light source 600 is focused on a pinhole 604 through a focusing lens 602 for spatial filtering, and is then incident upon a phase plate 606 having a predetermined phase structure, so that a hologram is formed on a hologram plane of a photosensitive medium 608 disposed at a position remote by a distance f 5 from the phase plate 606.
  • Fig. 16 (a) and (b) show an annular phase structure formed on the surface of the phase plate 606 serving as a superresolution filter.
  • Fig. 16 (b) is a section view taken along the line XVI-XVI in Fig. 16 (a).
  • a beam which penetrates the center area 606a of the phase plate 606 serves as the reference light mentioned
  • Fig. 17 (a) and (b) show an annular phase structure formed on the surface of a phase plate 610 serving as a superresolution filter as a modification of the phase plate 606.
  • Fig. 17 (b) is a section view taken along the line XVII-XVII in Fig. 17 (a).
  • the phase plate 610 is provided on the surface thereof with an inner annular concave groove 610a (the radius of the outer periphery: R 1 ) and an outer annular concave groove 610b.
  • an opaque area is formed except for a center area 610c (diameter: ⁇ ) comprising a circular transparent part.
  • annular area 610d Formed between the inner and outer concave grooves 610a, 610b is an annular area 610d comprising an annular transparent part.
  • ⁇ 2 is set to 2 ⁇ 1 in Equation (6) and R 2 is set to 2R 1 in Fig. 17 in an example of preparation of a holographic filter.
  • the principal light source reference light
  • such secondary harmonics are identical with an interference component of the second auxiliary light source with the principal light source. Accordingly, such secondary harmonics exert no bad influence upon the transmittance characteristics of the superresolution filter, i.e., the regenerated image characteristics of the holographic filter.
  • a distortion term generated in a normal hologram can be restrained to such an extent as to exert no substantial bad influence upon the characteristics required as a superresolution filter, when the ratio of the amount of light of the reference light source is sufficiently increased.
  • the effect (2) would be understood from the fact that the amount of light is not considerably lost except that a zeroth transmitted light through a holographic filter is emitted in an equivalent value from the principal light source of the superresolution light source, causing the light to become a beam, and this beam interferes with beams from the regenerated first and second auxiliary light sources, thereby to form a predetermined superresolution spot.
  • Fig. 18 shows a schematic arrangement of an example in which the superresolution filter above-mentioned is integrated with a plano-convex collimate lens 702 in a laser beam printer optical system using a polygon mirror 700.
  • a coherent light source 704 of a semiconductor laser there are also shown a coherent light source 704 of a semiconductor laser, a focusing lens 706 and a superresolution spot 708.
  • a replica 710 made of glass or resin serving as a superresolution filter is bonded to the flat face of the plano-convex collimate lens 702.
  • such an arrangement may be made by forming a superresolution filter of glass or a plastic material integrally with the flat face of the plano-convex collimate lens 702.
  • a predetermined superresolution holographic filter may be applied to the collimate lens 106 in Fig. 1 or the collimate lens 206 in Fig. 4. It is a matter of course that the arrangement above-mentioned can be conveniently applied to any of a variety of conventional scanning optical systems such as laser scanning microscopes.
  • the superresolution holographic filter utilizes mere several interference patterns having an extremely long cycle as compared with a normal holographic optical element.
  • the interference patterns can be precisely calculated by a computer to obtain the phase profile of a phase hologram, and the phase profile thus obtained can be reproduced on glass or a mold by cutting or polishing the same. It is a matter of course that a superresolution filter can be formed on a collimate lens face in such a manner.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Artificial Intelligence (AREA)
  • Toxicology (AREA)
  • General Health & Medical Sciences (AREA)
  • Health & Medical Sciences (AREA)
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  • Theoretical Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Optical Head (AREA)
  • Holo Graphy (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)
  • Mechanical Optical Scanning Systems (AREA)
EP93104561A 1992-03-19 1993-03-19 Superresolution scanning optical device Expired - Lifetime EP0562488B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP4063761A JPH0695038A (ja) 1992-03-19 1992-03-19 超解像走査光学装置、光学装置の超解像用光源装置及び光学装置の超解像用フィルター
JP63761/92 1992-03-19

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DE69315871D1 (de) 1998-02-05
DE562488T1 (de) 1994-11-17
KR930020375A (ko) 1993-10-19
DE69315871T2 (de) 1998-04-16
EP0562488A1 (en) 1993-09-29
US5496995A (en) 1996-03-05
JPH0695038A (ja) 1994-04-08
US5978109A (en) 1999-11-02

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